The present invention relates to a control valve used for a displacement variable compressor incorporated in a refrigerant circuit of an air-conditioning system for controlling the discharge displacement of the variable displacement type compressor, which can change the discharge displacement in accordance with the pressure in the crank chamber.
Japanese Unexamined Patent Publication No. 6-341378 discloses such a control. This control valve mechanically detects the pressure difference between two pressure monitoring points, which are located in a refrigerant circuit, and adjusts the pressure in a crank chamber by determining the position of a valve body in accordance with a force that acts on the spool, based on the pressure difference.
In the control valve, the spool is displaced by sliding along the inner wall of a pressure sensing chamber according to the fluctuations of the pressure difference. Therefore, the sliding resistance between the spool and the inner wall of the pressure sensing chamber or a foreign particle caught in the sliding portion hinders the smooth movement of the spool. Accordingly, the fluctuations of the pressure difference is not promptly reflected on the opening size of the valve and the discharge displacement of the compressor. As a result, the cooling performance of the associated air-conditioning system deteriorates.
Accordingly, it is required to perform surface treatment such as smooth grinding and to form a low-friction coating to reduce the sliding resistance between the spool and the inner wall of the pressure sensing chamber. Alternatively, a filter must be provided in the control valve to remove foreign particles. As a result, the cost of the control valve increases.
The objective of the present invention is to provide an inexpensive control valve for a variable displacement type compressor that can promptly change the opening size of a valve according to the fluctuations of the pressure difference between two pressure monitoring points.
To achieve the foregoing objective, the present invention provides a control valve used for a variable displacement compressor installed in a refrigerant circuit of a vehicle air conditioner. The refrigerant circuit has a suction pressure zone. The compressor varies the displacement in accordance with the pressure in a crank chamber. The compressor has a bleed passage, which connects the crank chamber to the suction pressure zone. The control valve comprises a valve housing. A valve chamber is defined in the valve housing to form a part of the bleed passage. A valve body is accommodated in the valve chamber for adjusting the opening size of the bleed passage. A pressure sensing chamber is defined in the valve housing. A pressure sensing member separates the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The pressure at a first pressure monitoring point located in the refrigerant circuit is applied to the first pressure chamber. The pressure at a second pressure monitoring point located in the refrigerant circuit is applied to the second pressure chamber. The pressure sensing member moves the valve body in accordance with the pressure difference between the first pressure chamber and the second pressure chamber such that the displacement of the compressor is varied to counter changes of the pressure difference. The pressure sensing member is a bellows or a diaphragm.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.